The incidence of diseased and healthy Silene virginica along ca.
The number of diseased and healthy plants was counted in nine populations (defined as clearly distinct patches) of Silene virginica, for 4 yr (1989-1992).
We recorded the numbers of diseased and healthy Silene virginica in several populations in the Korstian Division of Duke Forest, Orange County, North Carolina, for 4 yr (1989-1992).
Diseased populations of Silene virginica were found in all three study areas (Tables 2-3).
The occurrence of the disease in Silene virginica was extremely patchy (Table 2).
In 1988, when we found the anther-smut disease of Silene virginica near to diseased populations of S.
violacea on Silene virginica made a host shift onto S.
The distributional and demographic studies reported here do not support the idea that the disease on Silene virginica is spreading rapidly as a pandemic and threatening population of the host.
The spatial discontinuity in disease incidence in Silene virginica was qualitatively similar to that found in S.
Perhaps, all Silene virginica plants pass through a period of susceptibility as preflowering juveniles, but are resistant as adults; plants that display such "adult plant resistance" are well-known in agriculture (Burdon, 1987).
Although nothing is known about disease resistance in Silene virginica, the presence of resistant genotypes in S.
If vegetative infection is the predominant mode of disease transmission, then the dynamics of anther-smut on Silene virginica may be governed more by density-dependent transmission, rather than by frequency-dependent transmission as in S.
In spite of the common occurrence of the anther-smut on Silene virginica and S.